Rocket fuels containing nitrated



2,982,636 Patented May 2, 1961 ice ROCKET FUELS CONTAINING NITRATED HYDROXYLATED POLYMERS William B. Reynolds, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Apr. 14, 1952, Ser. No. 282,279

19 Claims. 01. 52-.s

This invention relates to fuels particularly suitable for use in jet propulsion motors. In one aspect-this invention relates to solid rocket propellants. In'another aspect this invention relates to selected nitrated hydroxylated poly- I mers particularly suitable as fuel components of rocketpropellants.

ucts of combustion must escape, and in escaping, provide, a propulsive force. In one of the most convenient types of such motors, a solid fuel is employed, the solid charge to the system comprising an intimate mixture of a solid fuel with a solid oxidizer, the said fuel acting also as a binder for the charge. This fuel oxidizer mixture is cast or molded into a suitably shaped charge which is stored in the combustion chamber, thus avoiding the need for complicated feeding-arrangements. The form of this charge is preferably such that a substantially constant burning area will be provided during the propulsion period. Thus the propulsion force or thrust will be maintained at a substantially constant value as the charge burns. Such constant burning area can be realized by forming the charge in any one of several configurations having one or more surfaces which will remain constant during the propulsion period, other surfaces being re-.

stricted by suitable means. The charge can be formed prior to being introduced into the burning chamber or may be formed in the chamber itself. When formed outside the burning chamber, restriction of areas where burning is not desired is eifected by wrapping or otherwise coating with an impervious material which may, if desired, be a portion of the binder in which there is no oxidant. When'the charge is formed in the burning chamber, the wall of said chamber can act as the restricting means. It is frequently preferable to coat the interior of the burning chamber with a protective material. Such protective material can be a portion of the binder with which no oxidant has been admixed.

In accordance with this invention I have provided nitrated hydroxylated polymershaving the especial utility as rocket fuels, i.e., as fuel components of rocket spropellants and also being particularly suitable as binder materials when employed in conjunction with various rocket oxidants.

the preparation of nitrate esters of this invention are characterized by having a number average molecular weight of at least 350 and ranging as high as 500,000 and in some cases higher, and by an iodine number (Wijs or modified Wijs method-grams iodine per 100 grams sample) within the range of 150 to 625. The average molecular weight is determined by some suitable absolute method, for example the molecular weight can be determined by the freezing point lowering of benzene method on those materials with a molecular weight of 350 to 2000, and by the osmotic pressure method on materials with a molecular weight from 2000 to 500,-. 000. Included among such olefinic starting materials are high-boiling residues from petroleum refining processes such as are formed during thermal and catalytic cracking operations and during clay treating and: acid treating of cracked naphthas, and, catalyst-soluble oils formed as by-products during the conversion of hydrocarbons in the presence of hydrofluoric acid as a catalyst, particularly in a process involving the reaction of an isoparafiin with an alkylating reactant such as propylene, various butylenes, amylenes and olefinic mixtures boiling up to 500 F. Other important olefinic starting materials include conjugated diolefin liquid polymers and copolymers, i.e., free from solid polymers, e.g., liquid polybutadiene, liquid polyisoprene and liquid copolymers of diolefins with other monomers copolymerizable therewith prepared by either mass or emulsion polymerization. Other suitable polymeric starting materials includerubber-like polymers and copolymers of conjugated diolefins. The said copolymers are formed with such compounds as styrene, alkyl-substituted styrenes, acrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, and the like.

Hydroxylation of the polymeric olefinic starting material can be'accomplished by any suitable means. One method comprises treatment of the olefinic starting material with hydrogen peroxide in the presence of a hydroxylation catalyst such as formic acid or a selected lower alkyl ester thereof such as methyl formate, ethyl formate or the like. The production of hydroxylated liquid polydienes by this method is described in the copending application of J. C. Hillyer and J. T. Edmonds, Serial Number 204,062 filed January 2, 1951, now Patent Number 2,692,892. In that copending application is described the hydroxylation of a liquid polymer of 1,3-butadiene.

When a liquid polymeric olefinic starting material is employed for hydroxylation and subsequent nitration,

These polymeric materials are prepared by hydroxylat- 7 hydroxyl groups. Thus the hydroxylated polymeric prod-- uctcontains a plurality of the characteristic group:

- sired hydroxypolybutadiene.

such material is characterized by its low molecular weight usually less than 5000 and preferably less than 2000 (determined by freezing point lowering of benzene), and its appearance as a pale yellow liquid having a viscosity in the range of 100 to 6000 Saybolt Furol seconds at 100 F. This liquid polymer can be prepared by'sodium catalyzed polymerization of 1,3-butadiene. One method for the preparation of such a liquid polybutadiene, free from dissolved solids, is fully described in the copending application of W. W. Crouch, Serial Number 67,098, filed December 23, 1948, now US. Patent 2,631,175, issued March 10, 1953. In accordance with the hydroxylation procedure as disclosed in the said copending application of Hillyer and Edmonds, such a liquid polybutadiene is hydroxylated by reactionwith hydrogen peroxide or a compound capable of yielding hydrogen peroxide with or without a solvent in the presence of a catalyst, for example formic acid, under time-temperature conditions suflicient to yield the de- Preferred hydroxylation 7 conditions include a temperature in the range of 10 to C. and a reaction time generally within the range from 1 to 60 hours.

In the hydroxylation of the polymeric olefinic start- 3. ing material in accordance with the preparative method of the present invention, the hydroxylation is effected under conditions which will generally hydroxylate at least 10 percent of the double bonds of the polymeric reactant and preferably 20 percent or more. Generally, I prefer to hydroxylate not more than about O percent of the double bonds.

Nitration of the hydroxylated product can be accomplished by any' suitable means, such as with a nitrating mixture comprising fuming nitric acid and acetic anhydride. Temperatures in the range from to +l0 C. are frequently preferred. A solution of the hydroxylated polymer is gradually brought. into contact with the nitrating mixture and sufiicient time is allowed for completion of the reaction. The quantity of nitrating agent employed is preferably suflicient to react with at least 25 percent and can be sufficient to react with sub stantially all of the hydroxyl groups present.

The polymeric nitrate esters of this invention can be compression molded and employed as rocket fuels or can be intermixed with solid oxidants and compressed, or the resulting mixture can be cast from a molten state to any desired solid form. Further, they can be employed as binders in any given rocket propellant, i.e. to support the oxidant-fuel admixture as a single solid body.

Well-known oxidizers that can be employed with solid rocket fuels can be employed in conjunction with the polymeric nitrate ester fuels of this invention as rocket propellants. Included among solid oxidizers that can be employed are nitrates, perchlorates, chlorates, chlorites, hyprochlorites, dichromates, chromates, and persulfates, preferably as the potassium, sodium and ammonium salts. Salts of other metals such as calcium, magnesium, aluminum and the like may also be employed.

In the preparation of the propellant mixtures of this invention, the oxidizer is admixed with the polymeric nitrate ester fuel component, each being in a finely divided state so that a substantially uniform mixture is obtained. The propellant mixture of this invention can comprise the fuel components commingled with the finely divided oxidizer, in proportions preferably such that the fuel is present in molal excess, i.e. an excess in the amount which would be consumed by the oxidizer under theoretical conditions of complete combustion. Accordingly, a suitable proportion of the oxidizer in the propellant mixture would be from about 50 to 90 percent of that which would be required for the complete combustion of the fuel to carbon dioxide and water, although when desired, proportions of oxidizer above the said 90 percent can be employed, e.g. 100 percent.

When employing the polymeric nitrate ester fuel as a component of a rocket propellant, the fuel contains a relatively large number of nitrate ester groups, e.g. resulting from nitration of from 35 to 90 percent of the hydroxy groups of the hydroxy polymer. However, products which contain a relatively smaller number of nitrate ester groups, such as from nitrating polymers of a low degree of hydroxylation, or partially nitrating materials having a high degree of hydroxylation can be used satisfactorily.

Hydroxylated polymeric materials of the type discussed above, of relatively low molecular weight and which are partially nitrated, can be condensed with materials such as maleic anhydride, phthalic anhydride, diisocyanates, or the like, and then employed in a rocket propellant, or can be further condensed to produce polyurethane resins which are suitable for use as rocket propellants. Such condensation reactions can be effected in the presence of solid oxidizing agents such as ammonium or potassium perchlorate, or ammonium nitrate.

Illustrative of the catalyst-soluble by-product oils that can be employed as polymeric olefinic starting materials inthe preparation of polymeric nitrate ester fuels of this invention are the I-I-F-acid soluble oils formed as a byproduct of a parafiin-olefin alkylation process of the type mixture of ice and water.

- 4% already described, characterized by properties tabulated as follows:

Properties of HF-acid soluble oil API gravity 60 F. 10-30 Viscosity, SUS, F 100-1000 Viscosity, SUS, 210 F.1 40-80 Flash point, coc, F? 190-250 Fire point, 000, P Fe 220-270 Pour point, F. 30-5+ Total solids, percent 65-80 Iodine number 5 -300 Aniline point, C. 30-100 Free HF None A.S.T.M. designation 446-39.

A.S.T.M. designation D9245.

A.S.i.M, designation D97.

A.S.T.M. designation D154.

5 Wijs method-gms. iodine/100 gins. sample. A.S.T.M. designation D611-44'1.

' A.S.T.M. designation D663-44T.

The clay tower polymers, i.e. the polymer product of polymerization treatment of unrefined cracked gasolines are illustrated with respect to the following tabulation setting forth various physical properties thereof.

Percent nonvoiatiles as measured at 225 F. for a duration of 3 hours.

VVijs-grams iodine that will react with 100 grams of sam 1e.

3 STM designation 446-39.

4ASTM designation D9245.

ASTM designation D-97.

By way of the following example, I have illustrated one method by which a polymeric nitrate ester fuel of my invention can be prepared.

A S-gram sample of liquid hydroxypolybutadiene, having a molecular Weight of 850, an oxygen content of 18.25 percent, and hydroxyl number of 550, indicating that approximately 26 percent of the double bonds in the liquid polybutadiene starting material had been hydroxylated, was dissolved in 30 cc. of acetic anhydride. This solution was added slowly to a nitrating mixture containing 30 cc. fuming nitric acid and 30 cc. acetic anhydride, previously prepared and cooled to approximately 0 C. Addition of the hydroxypolybutadiene required 45 minutes. The mixture was stirred during this time and for an additional 30 minutes after which the reaction was considered complete. Temperature was maintained at 0-5 C. throughout the reaction.

The reaction mixture was poured into 400 grams of a The nitrated polymer which separated was filtered, washed free of acid with water, and dried. The product (8.5 grams) was a light yellow powder which burned readily. The nitrogen content of the product was 11 percent.

The product was compression molded into pellets which has good burning characteristics.

Variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is the provision of (1) hydroxylated, nitrated polymeric .olefins, i.e. polymeric nitrate esters; (2) production of the said polymeric nitrate esters by the steps: (a) hydroxylating a polymeric olefinic compound; (12) nitrating the resulting hydroxylated polymer; and (0) recovery of a polymeric nitrate ester from the resulting reaction mixture; (3) rocket propellants containing the above said polymeric nitrate esters, or cross linked derivatives thereof as fuel components and/or binding agents; and (4) a method for making rocket propellants.

I claim:

1. As a solid rocket propellant, a polymeric nitrate ester, as a fuel component, prepared by hydroxylation of a polymeric olefinic material having a molecular weight of at least 350 and an iodine number in the range of from 150625 and by nitration of the resulting hydroxylated polymer, and a solid inorganic oxidizing salt admixed with said fuel component in an amount of from about 50 percent of that required for supporting complete combustion of the said fuel component to carbon dioxide and water up to that amount necessary for effecting substantially complete combustion of the said fuel component.

2. The composition of claim 1 wherein at least percent of the double bonds in said polymeric olefinic material are initially hydroxylated and wherein at least 25 percent of the resulting hydroxyl groups are nitrated to form nitrate ester groups.

3. The composition of claim 2 wherein said polymeric olefinic material comprises a liquid polybutadiene free from solid polymers.

4. A composition of claim 1 wherein said polymeric olefinic material is a catalyst-soluble oil formed as a byproduct during the reaction of a parafiin hydrocarbon with an olefin in the presence of hydrofluoric acid as a catalyst.

5. The composition of claim 1 wherein said polymeric olefinic material is a polymer product formed during the polymerization treatment of unrefined cracked gasolines to remove unsaturated materials therefrom detrimental to the use of said gasoline as a motor fuel.

6. In a solid rocket propellant comprising a solid inorganic oxidizing salt and a solid fuel component, the improvement providing as said fuel component a product of condensation of a nitrated hydroxylated polymer of an olefinic compound with a material selected from the group consisting of maleic anhydride, phthalic anhydride, and a diisocyanate.

7. As a solid rocket propellant, a nitrate ester of a hydroxy polymeric olefinic compound as a fuel component in admixture with a solid inorganic oxidizing salt in an amount of from about 50 percent of that required for supporting complete combustion of the said fuel to carbon dioxide and water up to that necessary for elfecting substantially complete combustion of the said fuel.

8. As a solid rocket propellant, a fuel component prepared by hydroxylation of a liquid polymer of a conjugated diolefin free from solid polymers and by nitration of hydroxylated polymer thus formed, and a solid in- 7 organic oxidizing salt admixed with said fuel component in an amount of fromabout 50 percent of that required for supporting complete combustion of the said fuel to carbon dioxide and water up to that necessary for effecting substantially complete combustion of the said fuel.

9. As a solid rocket propellant, a fuel component prepared by hydroxylation of a liquid polymer of 1,3- butadiene free from solid polymers and by nitration of hydroxylated polymer thus formed, and a solid inorganic oxidizing salt admixed with said said fuel component in an amount of from about 50 percent of that required for supporting complete combustion of the said fuel to carbon dioxide and water up to that necessary for effecting substantially complete combustion of the said fuel.

10. A composition of claim 9 wherein at least 10 percent of the double bonds in said liquid polymer are hydroxylated and wherein at least 25 percent of the resulting hydroxyl groups are nitrated.

11. A composition of claim 10 wherein not mOfe than 50 percent of the said double bonds are hydroxylatedand from 35-90 percent of the resulting hydroxyl groups are nitrated.

12. As a rocket propellant a nitrate ester of a hydroxy polymeric olefinic compound as a fuel component in admixture with a solid inorganic oxidizing salt, present in an amount of from 50-90 percent of that required for supporting complete combustion of the said fuel to carbon dioxide and Water. 7

13. In the development of thrust in a combustion chamber of a rocket motor, wherein a solid rocket fuel is burned in admixture with a solid inorganic oxidizing salt to develop said thrust, the improvement comprising burning, as said fuel, a nitrate ester of a hydroxy polymeric olefinic material.

14. The improvement of claim 13 wherein said polymeric olefinic material is a liquid polymer of a conjugated diolefin, free from solid polymers.

15. The improvement of claim 14 wherein said conjugated diolefin is 1,3-butadiene.

16. The improvement of claim 14 wherein said polymeric olefinic material is a catalyst-soluble oil formed as a by-product during the reaction of a parafiin-hydrocarbon with an olefin in the presence of hydrofluoric acid as a catalyst.

17. The improvement of claim 14 wherein said polymeric olefinic material is a polymer product formed during the polymerization treatment of unrefined cracked gasolines to remove the unsaturated materials therefrom detrimental to the use of said gasolines as a motor fuel.

18. As a solid rocket propellant, a fuel component prepared by hydroxylation of a liquid polymer of 1,3- butadiene free from solid polymers and by nitration of hydroxylated polymer thus formed, the said liquid polymer having been prepared by mass polymerization, and a solid inorganic oxidizing salt admixed with said fuel component in an amount of from about 50 percent of that required for supporting complete combustion of the said fuel to carbon dioxide and water up to that necessary for eifecting substantially complete combustion of the said fuel.

19. As asolid rocket propellant, a fuel component prepared by hydroxylation of a liquid polymer of 1,3-

butadiene free from solid polymers and by nitration of hydroxylated polymer thus formed, the said liquid polymer having been prepared by emulsion polymerization, and a solid inorganic oxidizing salt admixed with said fuel component in an amount of from about 50 percent of that required for supporting complete combustion of the said fuel to carbon dioxide and water up to that necessary for effecting substantially complete combustion of the said fuel.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AS A SOLID ROCKET PROPELLANT, A POLYMERIC NITRATE ESTER, AS A FUEL COMPONENT, PREPARED BY HYDROXYLATION OF A POLYMERIC OLEFINIC MATERIAL HAVING A MOLECULAR WEIGHT OF AT LEAST 350 AND AN IODINE NUMBER IN THE RANGE OF FROM 150-625 AND BY NITRATION OF THE RESULTING HYDROXYLATED POLYMER, AND A SOLID INORGANIC OXIDIZING SALT ADMIXED WITH SAID FUEL COMPONENT IN AN AMOUNT OF FROM ABOUT 50 PERCENT OF THAT REQUIRED FOR SUPPORTING COMPLETE COMBUSTION OF THE SAID FUEL COMPONENT TO CARBON DIOXIDE AND WATER UP TO THAT AMOUNT NECESSARY FOR EFFECTING SUBSTANTIALLY COMPLETE COMBUSTION OF THE SAID FUEL COMPONENT. 